What is wrong with my Suzuki GS500 Motorcycle?

Question

It is having some sort of electrical problem. The GS500 is normally a reliable workhorse. The basic design has yet to change since it's inception in 1989. It's a 500cc, parallel twin, air-cooled, carbureted, 4-stroke. Basic stuff, no computers or fuel injection. Please answer in depth with explanation only if you have experience. 

I was riding one day and the engine stuttered and surged on me. I figured it was low fuel, so I changed to the reserve and refueled. The problem got progressively worse. When I ride it, I noticed when I use the turn signals, they flash irregularly - fast blinks, then slow, then fast for a while, then normal - no real pattern to it. When I idle, the headlight brightness flickers. The engine stuttering and surging has progressed to a serious bucking. When I try to ride it normally with constant throttle, it bucks like I'm constantly gunning it and then letting off. It then gave up all throttle response for a bit. I had to pull off the road. it would just linger around 1500 rpm and would not respond to choke or me revving the throttle. in about a minute it recovered enough for me to make it a 1/4 mile home. It starts and idles normally. It just doesn't respond to throttle. I don't think its a clogged petcock, I switched it to PRIME to bypass the diaphragm and it makes no difference.

It is a 2001 with only 9000 miles. I bought it with 7000 and and other than a small scrape on the engine case, a common thing with any bike (drop it once and you've got one) it appeared flawless. I've had it for 1 year and it ran like a dream with no problems up until now. The battery is not new, but not dead either. 

Here are my guesses: 
1) Bad electrical grounding: A common source of "gremlins"
2) Blown or corroded fuze: Just a guess
3) Voltage rectifier has gone bad: May explain the turn signals and the headlight and perhaps a sparking issue.
4) Ignition coil has gone bad: This usually only results in 1 of the 2 cylinders firing, but wouldn't a dead coil mean I get steady, but significantly reduced performance because it still runs like a 250cc single? It idles smoothly.

Firecracker . · Accepted Answer

Yes, that sounds electrical too me. Voltage fluctuation.
The trick is to find it.
Start at the battery, checking connections for both cleanliness and tightness (hot and ground).
Take them apart and put them together again.
Go all the way through, checking the plugs as well.
The 3 wire plug from the stator to the rectifier/regulator is a spot known to go bad.
Dirty connection causes heating resulting in melted plug and bad/no connection.

If this doesn't cure it, it's time to break out the meter and manual.
First thing, before doing any electrical tests, is to make sure that the battery is good and fully charged. The readings you get will not be any use if the battery is no good or discharged.

Brian M · Answer

I'd have to say it's part of the charging system.  That could be the battery (yes, they can and do just 'suddenly' go bad), a burned or loose wire/connection, the reg/rec or the stator.  My first guess is Always the battery, Occams Razor and all.

First things first, charge the battery with a 1amp/hour charger.  A "smart" charger is best as it can detect sulphate and pulse the charging power to help break it up a little (among other things).  With the battery full, hook up a multi-meter and head out on a ride while watching charging voltages.  If you see it drop Below 12.7vdc at any time, there's a charging issue.  You'll have to then check the Reg/Rec and the Stator to see which is the problem.

bikinkawboy · Answer

I'm with Brian, I'd try charging the battery and then check it with an inexpensive, floating ball hydrometer.  That should give you an idea if you have a dead cell of if the battery is taking a charge.  If the battery checks out ok, then you probably need to start pulling electrical connectors apart, checking for corrosion.  Especially check the ones at the voltage regulator as well as any that are near the battery vent tube.  Don't forget to check where the battery negative strap attaches to the frame and or engine.

Anonymous · Answer

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RE:
What is wrong with my Suzuki GS500 Motorcycle?
It is having some sort of electrical problem. The GS500 is normally a reliable workhorse. The basic design has yet to change since it&#39;s inception in 1989. It&#39;s a 500cc, parallel twin, air-cooled, carbureted, 4-stroke. Basic stuff, no computers or fuel injection. Please answer in depth with...

Firestormer · Answer

You have some very good guesses there.
I would start with No.1 (It's the easiest) Check the connection of the main negative to the frame/engine. Even if it is tight, dismantle it and clean the contacting surfaces thoroughly. Do the same with the battery terminals

Continue to  work your way down your list.

Anonymous · Answer

Gs500 Battery

Candid Chris · Answer

My best guess is #3, but at 9K ?!? There is a test to check voltage from the rectifier but unsure as to a definite procedures on your bike.
Another thought is a clogged fuel delivery and you can pull the plugs to check firing that pretty easily.
And while at the plugs check the coils for spark.

mn · Answer

not here to answer the question... you have enough good answers to give you a start on the problem..

BUT had to come on & say HOOORAY...  a question with all the relevant info & background..

if only all the others on here knew how to ask a question..

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What is wrong with my Suzuki GS500 Motorcycle?

8 Answers